Spurious complaint about return value in deferred function

[JukkaL]

Mypy incorrectly complains about the return statement in this program (with --strict-optional):

def f() -> str:
    y  # Causes f to be deferred
    x = None
    if int():
        x = ''
    if x is None:
        x = ''
    return x  # Incompatible return value type (got "Optional[Any]", expected "str")

y = int()

The expected behavior is clean output.

Note that f is deferred. The problem goes away when f is not deferred.

[JukkaL]

Slightly tweaked example illustrates another problem:

def f() -> str:
    y
    x = None
    if int():
        x = ''
    if x is None:
        x = ''
        x[0]  # Value of type "None" is not indexable   <-- Unexpected
    return x  # Incompatible return value type (got "Optional[Any]", expected "str")

y = int()